1. The Area of the Invention
The invention refers to advantageous constructions of ribbon-type loudspeakers.
2. Prior Art
The working principle of the ribbon speaker is well known. Inside a magnetic field, a ribbon made from an electrically conducting material is stretched, on both sides surrounded by powerful elongated permanent magnets. When an AC current within the audio band is applied to the ribbon, the membrane will start to oscillate in pace with the input signal.
The ribbon speaker technology suffers from two major problems: On one hand the linearity of the magnetic field is not homogenous; (typical solutions are glued ferrite magnets),—on the other hand the frequency response is not flat but decreasing with rising frequency, the last mentioned depending on the ribbon's mass/inertia and the inductance of the ribbon and the signal feeding cables. Last but not least, the width of the membrane has a serious impact on the ribbon amplitude. A wider ribbon results in a higher radiation resistance, i.e. a better coupling to the air, which means lower membrane amplitude which is essential if low frequencies with a satisfactory sound pressure level are to be reproduced.
Electrical Limitations:
The low electrical resistance of the ribbon speaker and its physical extension in space result in an inductance that seriously affects the frequency response and, most important, create serious phase errors. The preferred invention solves this problem by utilizing passive current feeding over the whole operating area below 1/f and also by a separate passive compensation feeding for the frequency range above the 1/f point.
The physical mass of the ribbon together with the strength of the magnetic field determines where the critical 1/f point occurs. This point is defined as the point where the ribbon goes from velocity-controlled to mass-controlled condition. Above this point, the ribbon output no longer is linear but decreasing with increasing frequency.
Mechanical Limitations:
The physical mass of the ribbon, combined with the strength of the magnetic field, determine, as earlier stated, where the critical 1/f point occurs. This point is defined as the point where the ribbon goes from velocity-controlled to mass-controlled condition. Above this point, the ribbon output no longer is linear but decreasing with increasing frequency.